Since the cat is out of the bag already, I won't spoiler tag my thoughts below.
I am generally displeased that Kirkman kept Billy and Ben around for this long time only to simply dispose of them.
I do however, like the message that it sent home:
1. The kids ARE being negatively impacted. This theme was started many issues ago when Carl started exhibiting passive behavior to the killing and the increasingly aggressive behavior, leading to his attempted rape. The kids behavior is just sending that message home.
2. It showed how different people react to the same situation. Carl is using his aggressive behavior to channel his issues to remain "sane"; whereas Ben suddenly snapped. Of course, we as the reader can only conclude to that fact because they have had no screen time and Kirkman doesn't do inner dialogue.
3. I forgot the names of the twin sisters that were killed by the inmate that later scarred Andrea...but I thought of them when Billy and Ben died. The sisters were victims as were Billy and Ben; only more sick and twisted.
4. After issue #6, it is clear to me that Carl's path will be violent one. It will be interesting to see how he progresses as a character...provided Kirkman just doesn't get rid of him.
In general, there have been opportunities for Kirkman to flesh out characters that he has missed. I hope he continues to "take chances" with his method of perspectives and story telling to do this...especially since the actual story line hasn't really progressed all that much since #48 (it seems like yesterday and it's already been 12 issues).
As a side note, I've noticed lots more cursing in the last few issues...which appear out of context with the characters built thus far. I'm ok with things changing and people changing, but it appears to be happening "across the board". I'm rationalizing that this is a very stressful time (yet when was it not) but it seems a bit out of place from where I sit.
A comment on Charlie's artwork...there are issues where every panel is supreme; early on a lot of it was more "rough"...in this issue I saw a good mix of the two...it was glaring to see many details missing on Andrea's face next to panels with great detail and angles.